Method and apparatus for surveillance using an image server

ABSTRACT

Methods and apparatus for an image server surveillance system provide for as control and coordination of cameras that may be widely deployed, analyzing data from multiple cameras, making data available in such a way that it can be efficiently transmitted over a network and can be easily displayed to potentially a large number of users, and displaying and controlling image data by existing client software.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of patent application Ser. No.09/482,181, filed 12 Jan. 2000 now U.S. patent ______ which claimspriority from U.S. provisional application Ser. No. 60/131,990, filedApr. 30, 1999, each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention is in the field of electronic circuits and camerasystems. More particularly, the present invention is directed to asystem for surveillance using digital images and image servers.

Many types of camera surveillance systems are known. Typical buildingsurveillance systems today capture analog video signals from one or morevideo cameras and transmit those signals to a security panel for viewingby security personnel. Deployment of such systems over a large area andmaking the video images available over a network can be problematicbecause of the large bandwidth requirements of the video signal.Monitoring of multiple analog cameras is also difficult; for example, ahuman viewer's attention may not be on the security panel or directed tothe correct camera image at the time an incident occurs. An, in general,the number of cameras a human can effectively monitor is limited. Whiletechniques for motion detection in surveillance systems are known, thecomplexity and expense of incorporating these techniques into analogsystems has limited the use of motion detection in many videosurveillance systems.

Another problem that arises in analog surveillance systems is storageand playback technology of analog video data. Typical security cameras,at a retail store for example, employ videotape technology whereinfull-motion video is continuously recorded, without regard to whether anincident of interest has occurred. Video tapes are retrieved and playedback on the rare occasions when an incident occurs. A major problem withsuch systems is that the videotapes are often recorded at the slowestspeed, giving the poorest image quality, and are repeatedly rerecorded.As a result, playback image quality is often very poor and when anincident does occur, investigators cannot get a clear enough image ofindividuals involved in the incident to make an identification. Inresponse to this problem, the Federal Bureau of Investigation hasestablished a laboratory program whose primary function is to help lawenforcement personnel enhance poor quality images from videosurveillance systems in order to aid in investigations.

It is known to make digitized video images available over the web forpresentation by a web browser. Generally, such systems periodicallyupdate a full-frame captured still image from a camera using a push(controlled at the server side) or a pull (controlled at the clientside) technology. Such systems have had a limited deployment to makeimages of such things as ski slope weather conditions, elephant housesat a zoo, or children at a day care center, available over the web usinga standard web browser. In some applications, such as the day carecenter, access to the image is password protected so that onlyauthorized viewers can receive the images.

One group of cameras and camera servers for these applications aremarketed under the brand name Axis. However, these installations aregenerally limited to single or a few cameras and do not have the abilityto be deployed as a flexible and fully functional surveillance systems.Standard Axis technology also generally relies on full-frame updatingand has only limited ability to reduce bandwidth of images.

A number of techniques are known for compressing digital videoinformation. Well known techniques for digital video include hardwareassisted techniques such as MPEG, DVI, Motion JPEG, and software-onlytechniques such as QuickTime, Video for Windows, RealVideo, or AVI. Someof these techniques include mechanisms for processing and transmittingdelta frame information, wherein delta frames encode information aboutpixels that have changed between one frame and another. However, thesecompression techniques for the most part are concerned with the qualityof reproduction of real-time video image and have not been optimized foruse in surveillance systems or for use in systems that do not containcustom video playback software or hardware.

What is needed is a flexible surveillance system that can capture imagedata from a number of digital cameras and make that data available toviewers in a variety of different ways. In some applications, what isfurther needed, is a surveillance system with a basic architecture thatis scalable, allowing for efficient installation, coordination, andcontrol of one, to a few, to thousands of individual cameras and one toa few to thousands of individual clients. Additionally, what is neededis an integrated system for digital surveillance that at every step ofimage processing optimizes images for easy storage, analysis,transmission, and presentation in a surveillance system.

SUMMARY OF THE INVENTION

Specific embodiments of the present invention address a number ofproblems associated with a digital camera surveillance system, such ascontrol and coordination of digital cameras that may be widely deployed,analyzing data from multiple cameras, making data available in such away that it can be efficiently transmitted over a network and can beeasily displayed to potentially a large number of users, and displayingand controlling image data by existing client software such as abrowser. According to the invention, these problems are addressed byproviding a flexible and scalable surveillance system and method; themethod and system according to the present invention can workeffectively in small installations with just a few cameras and only oneviewer to installations including thousands of cameras, widelydispersed, allowing for selectable viewing by many viewers.

In a specific embodiment, the invention consists of the followingfunctional elements:

(1) Multiple Frame Grabbers (FGs) that include one or more cameras,digital image capture circuitry, and low-level logic routines. In oneembodiment, an FG comprises a PC equipted with one or more off-the-shelfvideo capture boards, with each video capture board connected to acamera. The PC is programed according to the invention, to control thevideo capture functions and to perform low-level logic processing. FGlow-level logic processing generally includes one or more of thefollowing: short-term storage of full images, computing of differentialimages, computing differential scores for a current image, filtering ofgradual ambient light changes, and adjusting of camera characteristics.FGs have a communication interface to send full frames and differentialframes to a coordinator.

(2) One or more Camera Coordinators for receiving full frames,differential frames, and possibly other data from FGs, storing thisdata, and for adding a higher level of image processing. Coordinatorsgenerally include logic for one or more of the following: detecting andstoring an incident from one or more FGs, resolving incidents frommultiple FGs into an incident sequence; image recognition; logging andcataloging incidents according to a rules-based engine; generatingalarms to security personnel or a server, etc. A coordinator may alsoinclude an interface for sending control signals to the FG to controlbasic FG functions such as frequency of capture, focus, contrast, and,for moveable FGs, positioning.

(3) A Camera Server for providing an interface to one or more clientviewers. A server handles image presentation and may include logicallowing a client to pan and zoom the view of an image. A serverincludes logic to provide an intelligent interface to a client viewerincluding launching windows in the client viewer when incidents aredetected and updating open windows with differential frames and fullframes. A server may also include an interface for receiving commandsback from a client and forwarding those commands to a coordinator whenappropriate. In some embodiments, a server also provides a possibly highcapacity connection to the Internet, allowing potentially thousands ofviewers to view the same image.

(4) One or more clients for displaying images delivered by the server.In some applications, clients may also receive commands from a user andforward results of those commands back to a server. In variousembodiments of the invention, clients may be familiar, off-the-shelf,browser applications, such as Netscape Navigator or Internet Explorer,or clients may be proprietary applications. According to the presentinvention, where desired in a particular installation, bothoff-the-shelf and proprietary clients can simultaneously access imagedata.

According to the invention, these elements perform separable tasksappropriate to that element to allow for a flexible and scalablesurveillance system. The flexible system according to the inventionallows various data and image processing tasks to be easily incorporatedinto specific systems depending on application. In security surviellancesystems where later authentication of a recorded digital image isimportant, for example, cameras and FGs can employ digital signature keytechnology or other technology to verify that an image was not alteredafter it was initially captured.

A further understanding of the invention can be had from the detaileddiscussion of specific embodiments below. For purposes of clarity, thisdiscussion refers to digital devices and concepts in terms of specificexamples. However, the method and apparatus of the present invention mayoperate with a wide variety of types of digital devices. It is thereforenot intended that the invention be limited except as provided in theattached claims. Furthermore, it is well known in the art that logicsystems can include a wide variety of different components and differentfunctions in a modular fashion. Different embodiments of a system caninclude different mixtures of elements and functions and may groupvarious functions as parts of various elements. For purposes of clarity,the invention is described in terms of systems that include manydifferent innovative components and innovative combinations ofcomponents. No inference should be taken to limit the invention tocombinations containing all of the innovative components listed in anyillustrative embodiment in the specification, and the invention shouldnot be limited except as provided in independent embodiments describedin the attached claims.

The invention will be better understood with reference to the followingdrawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an illustrative embodiment of the invention usingrepresentative hardware elements as it might be deployed in a moderatelysized business or academic setting.

FIG. 2 is a diagram of an alternative embodiment of the invention usingrepresentative hardware elements as it might be deployed at a singlelocation, such as a single moderately sized building.

FIG. 3 is an illustrative functional diagram of an embodiment of theinvention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS Overview of Two TypicalEmbodiments

Example Embodiment for a Large Campus

FIG. 1 shows an illustrative specific embodiment of a surveillancesystem according to the invention. Such a system consists of a number offrame grabbers (FGs) 10, each of which include one or more digitalcameras 12 and controller 14. FGs are in communication with coordinator20, which may coordinate one to many FGs. Coordinator 20 typically willinclude frame and incident storage 22 and may include rules storage 26.Coordinators 20 communicate with server 30, which will typically includeserver image storage 32 and client interface 34. Interface 34communicates with one or more viewing clients 40-42. Client 40-42 may bestandard, off-the-self client software allowing display of images andrunning on an appropriate computing device, such as a PC or workstation,web-capable television, etc. Well-known, currently available, browserclients include Netscape Communicator and Internet Explorer. One or moreof clients 40-42 may also be propriety client programs and may includespecialized hardware, such as panel 42, which may be a securitysurveillance panel or a kiosk display.

Connections 50 are shown in FIG. 1 to illustrate a functional datapathway between components. As is known in the art, such pathways can benetwork connections, backplane bus connections, wireless connections, ICinterconnects, or any other data channel appropriate for a particularembodiment hardware configuration of the invention. According to theinvention, the elements shown in FIG. 1 may be embodied in physicallyseparable electronic devices, or alternatively, the elements may beembodied into a small number of more integrated physical devices. FGs10, for example, may be constructed as a single electronic unit, withthe camera and controller component sharing some of the same logiccircuits. In some installations, some or all of coordinators 20 mayexist as processes on the same computer that holds server 30.Conversely, as is known in the art, server 30 or coordinator 20 may bephysically constructed of a number of closely cooperating computerhardware devices. Thus, FIG. 1 can be understood as an illustration offunctional elements of the invention with functions performed ondifferent arrangements of hardware components as appropriate to aparticular installation.

Example Embodiment for a Small Site Installation

FIG. 2 shows an alternative illustrative embodiment of a surveillancesystem according to the invention using a single computer 100 as ahardware platform. In this system, frame grabbers include one or moredigital cameras 12 and video capture boards 13. Other functions ofcontroller 14 are performed by logic running on computer 100.

Capture Boards 13 are distributed in bus slots in the computer andcommunicate with the camera either through a direct line or via wirelesstransceivers. Coordinator 20 exists as logic routines running oncomputer 100, using storage of the computer for frame and incidentstorage and any rule storage. Server 30 is also a process running oncomputer 100.

A client process 40 may also in some embodiments run on computer 100 toallow local viewing of captured images. Typically computer 100 will alsohave an image server 30 for remote client viewing. Interprocesscommunication in computer 100 allows for data exchange and in some casesdata sharing between the various functional elements.

Components of a Surveillance System

Frame Grabber Camera

FG 10 includes an off-the-shelf or custom camera 12 capable ofcooperating with other hardware to produce a digitally encoded imagearray. Many different types and brands of such cameras are available.Some of these cameras include a microphone and wireless transmissioncapability between the camera and the capture circuitry. For example, acurrently available off-the-shelf Remington™ brand audio/videosender/receiver combination allows for image/audio capture at low luxand wireless transmission to a capture board. Many such cameras employeither well-known CCD or CMOS technology to capture a digital image. Itis expected that an even wider range of such cameras will be availablein the future, with greater capabilities that will make themparticularly suitable for use in some embodiments of the presentinvention. Camera hardware often includes “steady cam” technology thatperforms some corrections for vibrations of the camera.

In one desirable embodiment, camera 12 will generally be non-moving(i.e. fixed) and will be located to capture a view of interest. As isknown in the art, camera 12 can be fitted with a wide-angle or “fisheye” lens to allow it to capture a large area. In such a case, softwarein the FG or in the coordinator or in the server is used to removedistortion caused by the lens and to flatten the captured image forviewing.

In some embodiments, an FG captures an image of a larger area than willtypically be displayed at one time at a client. Logic routines in eitherthe FG, the coordinator, or the server allow a client viewer to pan andzoom a view of the captured image.

Some capabilities of FG cameras that are either presently available orare anticipated soon to be available are the ability to capture framesof 15 million pixels allowing for greater zooming capability; theability to operate at very low light levels, and the ability to captureinfrared radiation or other non-visible electromagnetic radiation andthe ability to capture synched audio data. Camera hardware oftenincludes “steady cam” technology that performs some corrections forvibrations of the camera.

As is known in the art, CCD-type video digital cameras generally producean analog video scan signal, which must converted to digital for digitalprocessing or storage. However, it is expected that cameras willincreasingly become available that produce a byte-stream or bit-streamdescription of the detected image.

Frame Grabber Controller

Image Capture and Standard Image Encoding

Controller 14 includes capture circuitry and low-level processing andcontrol logic immediately associated with the camera to allow for anefficient and flexible overall system. In one embodiment, controller 14may be a PC-type microcontroller with an off-the-shelf, programmable,video capture board. In an alternative embodiment, controller 14 mayinclude or be comprised of custom designed logic circuits. Controller 14captures, and for a short time stores, sequential still images from thecamera in the form of digital data. For analog output cameras,controller 14 converts the analog signal to digital.

As is know in the art, video capture boards receive a video signal andconvert it to still digital frames at a selectable frame rate.Generally, the still digital frames are encoded as full-color images andthe capture board may perform some low-level color and brightnesscorrection of the received signal. The capture board delivers, ondemand, digital captured frames. In some capture boards, the imagedelivered is compressed and converted to an encoded format such as GIFor JPEG while in others only 24 bit color is possible. Off-the-shelfvideo capture boards brands include Videum and ATI.

Digital encoding of images can take many different forms. Onewell-known, uncompressed form for full-color digital images is a twodimensional array of numerical pixel values, with each pixel holdingthree 8-bit numerical values, one value indicating Red intensity, oneGreen, and one Blue. Thus, each pixel requires 24 bits of data and canrepresent one of 2²⁴ (16 million) different colors and an uncompressed,24-bit image with an image size 640×800 pixels requires 1.5 Mbytes ofstorage. Other encoding schemes are known, such as schemes that usefewer bits for each color value, and schemes that use different numbersof bits for different colors.

One well known technique for image compression can be generally referredto as the table/substitution technique. In this technique, the totalnumber of colors actually displayed in a single image is reduced from 16million to a smaller number, such as 256. A palette or table is createdby analyzing the original 16 million color image and selecting 256 ofthose colors for display. Those selected 256 colors are then stored in a256 entry indexed palette and the index number (in one known method, an8-bit number) for a color is substituted as the pixel value for thatcolor. The substituted pixel image and the palette are then used torepresent the image, reducing a 1.5 Mbyte image to closer to 0.5 Mbytes.In many known encoding formats, compression techniques are used tofurther reduce the storage needed for an encoded image. In sometable/substitution schemes, certain table values are reserved forpredefined colors. Pure black and pure white are commonly reservedcolors. In some schemes, a value is also reserved for a transparentpixel.

Processing Captured Frames

Once an image is captured, the FG controller processes the capturedimage and determines whether to send to the camera coordinator a fullframe, a computed differential frame, or no frame. This determinationmay be based the amount of change between the captured image and apreviously transmitted image, the elapsed time since the previoustransmit, the number differential frames sent since the previous fullframe, or other criteria. In one embodiment, a frame grabber alsotransmits differential scores that indicate an amount of change in thecurrent frame from the previous frame.

A number of variations in the processing of captured images to generatedifferential frames are possible according to the invention, andprocessing steps can take place in various orders or in parallel. Forease of understanding, the following description is provided of anexemplary specific embodiment processing.

Basic processing according to the invention involves a reference frameand a current frame, which are generally images of the same size andsame encoding. The current frame is the frame newly captured by thecapture board. The reference frame is a frame held in memory at thecontroller to which the current frame will be compared.

Computing Differential Scores

A differential score is determined for a current frame by determiningwhich pixels in the current frame have a different value from thecorresponding pixels in the reference frame. A number of variations incomputing and expressing differential scores are possible. A rawdifferential percentage score may be computed by comparing each bit inthe current frame to the corresponding bit in the reference frame. Ifthere is any difference in value, that pixel is considered a changedpixel. The ratio of the sum of all changed pixels to the total number ofpixels in the image is the raw differential percentage score.

A differential percentage score may also be computed using thresholdlogic routines to filter out differences between pixels that are not ofinterest, such as when a change is of minor intensity, or only affects avery small area. Threshold algorithms can be defined in a variety ofways appropriate to the particular overall image conditions andapplications. Thresholds can be defined that are different for differentcolors, such that a change in a green or red value, for example, is morelikely to cause a pixel to be counter as different than a change in ablue value.

In a further embodiment, the controller may analyze an image by dividingthe image into cells of roughly 5×5 pixels and determining the number of5×5 cells in the current image that have changed compared to thereference image and generating a differential score from thiscomparison.

In a further embodiment, threshold logic can compare a current frame tomore than one previous frames in order to determine whether capturedvalues are “flickering” while the actual image before the camera isunchanged. Such flickering is common in low light situations.

The controller may compute more than one type of differential score foran image. A differential score may be used by the controller todetermine whether or not to transmit a frame according to thecontroller's rule set and whether or not the controller believes anincident has occurred. One or more differential scores may betransmitted along with frames transmitted by the controller to thecoordinator.

Creating Differential Frames

A differential frame is constructed of the same size as the capturedimage and a reference image, using the same or a similar file format. Inthe differential frame, pixel values from the current frame that areidentical to or within tolerances of the reference frame are set to avalue indicating transparency and pixels that have changed retain thevalue from the newly captured image. This allows for a high compressionof the differential frame and for easy updating at a client viewer bysuperimposing a series of differential frames over a displayed fullframe, as discussed below. Once the differential frame has beenconstructed, the controller can perform a still image compressionroutine. In many image formats, this compression routine is built intothe format.

Other Controller Operation

As can be seen from above, in a simple and compact embodiment, acontroller can operate with only two full frames in memory, a currentframe and a reference frame, and a buffer for holding differentialframes. As discussed above, in an alternative embodiment, the controllermay retain additional image files to maintain a history of imageprocessing for retransmission purposes or for more involved thresholdand image analysis.

The process of computing one or more differential scores andconstructing a differential frame may be combined such that as thecontroller scans the pixels in the captured image frame, it computesdifferential scores and builds a differential frame.

From time to time, and whenever requested by a coordinator, a controllerwill transmit a current full frame. Among other functions, this allowsthe coordinator to catch up pixels that changed so gradually over timethat they never registered as differential pixels. In one embodiment, afull frame is sent every 10 images.

The controller logic may perform a number of other image processingfunctions as known in the art, such as converting the captured visualimage into a different format. One format that may be advantageouslyused is the well-known GIF format for encoding and compressing digitalimages. Other suitable formats include PNG, JPEG, etc.

Moving Camera

In a preferred embodiment of the present invention, the camera ismotionless. This allows for simpler control and processing logic and foreasier detection of incidents and computation of differentials. Anypanning or zooming for viewing the image is accomplished not by thecamera itself, but by logic functions closer to the client viewer, asdescribed below.

In an alternative embodiment, the invention may include moving ormoveable cameras. When a camera is moving, techniques that take intoaccount movement of the camera are used to compute the differential orcomputing of the differential can be suspended during camera movementand full captured images can be transmitted.

Camera Coordinator

Coordinator 20 receives frame data and possibly other control data fromone or more FGs. According to one embodiment of the invention, framedata is in the form of still images, including full (update) frames anddifferential frames and may include differential scores from some or allframes. Control data may include data indicating that the FG detected adifferential. It may also include data indicating the current positionor focus depth of a moveable FG, an FG identifier, and a time signal.Transmission of frames to the coordinator can take according to one ormore of the following: at expiration of a time interval since the lasttransmission, upon detection of a difference at a controller, at therequest of the coordinator.

Coordinator 20 in one embodiment also may send commands to the FGs tocontrol aspects of frame acquisition or transmission. Such commands mayinclude a resend, change camera characteristics such as brightness orcontrast, send a full frame, set the frequency for frame transmission,establish rules regarding when frames should be transmitted, establish atolerance level for determining if a differential frame should betransmitted, etc.

In a particular embodiment, the coordinator will include an interfaceallowing a user to program certain features of the controller, such asindicating regions of the visual field that should be processeddifferently. For example, the coordinator might be able to receive usercommands allowing a user to indicate that pixel changes in certainregions, such as windows or doorways, are not of interest during certainhours.

In one embodiment, a coordinator is primarily responsible fordetermining if an incident occurred. The coordinate accomplishes thisusing a rules-based engine or similar logical process that may take intoaccount time of day, day of the week, nature of the pixel changedetected, etc. In determining that an incident has occurred, thecoordinator takes into account differential scores transmitted by theFG.

In one embodiment, the coordinator also provides the principal incidentand history database for its connected cameras and includes the abilityto playback stored incidents. In further embodiments, the coordinatoradditionally has the ability to connect multiple incidents, triggered atmultiple cameras, into an incident sequence. The coordinator haspositional and view information about each camera and information aboutoverlapping regions of cameras. A coordinator will generally include alarge amount of longer term, non volatile storage, such as large diskdrives or removable storage technologies such as tape, or write/once orr/w CDs or DVDs.

In embodiments with a large number of cameras, a coordinator will be awork horse machine accomplishing much of the computation-intensiveprocessing needed by the system. As a result, a coordinator in such asystem may be constructed of a number of cooperating computers or amulti-CPU computer system. A coordinator handles the principaltime-stamping function for frames or incidents.

The coordinator includes a management interface to a management station26, which may be local to the coordinator or may connect remotely. Themanagement interface allows a user to perform various managementfunctions, such as setting time parameters for whether incidents fromparticular cameras will be of interest, establishing other rulesdefinitions. Alerts regarding cameras that have not reported in for awhile (exception) report generation. Installing new software and othermaintenance functions. The management station reports on itsinteractions with the camera server, such as cameras that have beenaccessed and how frequently and it receives commands from the cameraserver.

The coordinator can also perform advanced image processing tasks such asimage recognition or tracking a person or object identified in an imageor determining that an object is coming toward or moving away from thecamera. The camera coordinator sends commands to the camera serverregarding detected incidents or changes of an image that allow theserver to intelligently control the view of connected clients bychanging the view of images displayed at the clients or by creating newwindows and directing images to those new windows.

Image Server

A principal function of image server 30 is image delivery to clientsoftware for presentation to an observer. In a particular embodiment,the server can force a client to create new windows and can directincidents to different windows. In a preferred embodiment, the serveremploys push technology, wherein the server can periodically deliver adifferential image to the browser. The server's delivery of full imagesand differentials allows a client viewer to display a pseudo real timerepresentation of the image seen by the camera by overlaying thedifferential images on the existing displayed image, with a minimum ofprocessing and a minimum of transmission between the server and theclient.

A server includes cache storage and may keep a current full frame inmemory for all active attached cameras so that the server can transmit afull frame on demand when a client requests it. The image servertypically includes software with the ability to perform pan and zoomfunctions of an image.

In one embodiment, a server has the necessary logic to talk to Javacode, or similar code, running in the client. This allows a server todetermine if it should send a new image, such as to a newly connectedclient. The newly connected client will receive a full frame and enoughdifferential frames to get synchronized with the current view.

Prior art systems for transmitting moving images such as mpeg or theI-see-you,-you-see-me system suffer from utilizing a more complexencoding scheme requiring more specialized hardware and softwareinterfaces on both the captured end and the received end. The presentinvention benefits from the wide distribution of image viewing systemsusing simple static image coding in compression formats.

It receives commands from the client that it passes on to thecoordinator. Requests for information. Initiate of image streams.Termination of last image stream.

According to the invention, a surveillance system may be built with alow-speed/low-bandwidth connection between the FGs and the coordinator,a high-speed/high-bandwidth connection between the coordinators and theserver, and low-speed connections with individual clients.

Client Viewer

In one embodiment, client viewers 40 can include off-the-shelf PC'srunning off-the-shelf internet browsers. Preferably, the browsers willbe JAVA-enabled to allow image server 30 to switch views or create newwindows.

Clients can also include custom surveillance consoles, such as 42. Theseconsoles can coexit in a networked environment with other viewers.

FIG. 3 is an illustrative block diagram showing exemplary frame handlingaccording to a specific embodiment of the invention. It will be clear tothose of skill in the art that many variations in image and framehandling within the scope of the invention are possible.

1. A method for surveillance comprising: capturing a plurality of stillframes; generating, from said plurality of still frames, a sequence ofdigital image arrays comprising a full frame and a plurality ofdifferential frames; transmitting said sequence to a camera coordinator;determining, using said sequence, whether an incident is associated withone or more frames in said sequence; transmitting said sequence to animage server; storing said sequence at said image server; and providingsaid sequence to one or more clients for viewing by a user.
 2. Themethod according to claim 1 wherein said sequence stored at said imageserver is stored in a format designed for still image display on aclient browser.
 3. The method according to claim 1 wherein said sequencestored at said image server is stored in a format allowing for a pixelto be encoded as a transparent pixel.
 4. The method according to claim 1wherein said sequence stored at said image server comprises a full frameand one or more subsequent differential frames wherein pixels in adifferential frame with values within a threshold of correspondingpixels in a preceding frame are set to transparent.
 5. The methodaccording to claim 1 wherein said generating creates a sequence of fulland differential frames in a format designed for still image display ona client browser and allowing for a pixel to be encoded as a transparentpixel.
 6. The method according to claim 5 wherein said sequence istransmitted to said camera coordinator, stored at said cameracoordinator, transmitted to said image server, stored at said imageserver, and viewed by a client all using an image encoding format forstill image display on a client browser and allowing for a pixel to beencoded as a transparent pixel.
 7. The method according to claim 2wherein said format is the PNG format.
 8. The method according to claim2 wherein said format is the GIF format.
 9. The method according toclaim 1 wherein said deriving comprises computing a percentage value fora differential frame indicating a calculated percentage change betweensaid differential frame and a preceding frame.
 10. The method accordingto claim 1 wherein said determining comprises comparing a single stillframe to a preceding frame.
 11. The method according to claim 1 whereinsaid deriving includes computing a percentage value for a differentialframe indicating a calculated percentage change between saiddifferential frame and a preceding frame.
 12. The method according toclaim 1 wherein said clients comprise off-the-shelf internet browsersoftware.
 13. The method according to claim 1 further comprising:storing said sequence at said camera coordinator.
 14. The methodaccording to claim 1 wherein said storing comprises storage of sequencesfor which incidents were detected for later transmission as requested byan image server.
 15. The method according to claim 1 wherein said imageserver includes a network interface with a high bandwidth capacityallowing for multiple simultaneous client connections.
 16. A method forsurveillance comprising: capturing a plurality of still frames as arraysof digital data; designating a frame in said plurality as a full frame;for a frame subsequent to said full frame, computing a differentialframe wherein a pixel in said differential frame that is within athreshold of a geometrically corresponding pixel in a preceding frame isset to transparent; for a frame subsequent to said full frame, computinga percentage difference indicating a degree of change of pixels from apreceding frame; transmitting a full frame, one or more differentialframes, and one or more computed percentages to a camera coordinator;determining that an incident has occurred using rules-based logic toanalyze data received from said frame grabber; storing frame data, imagedata, and incident data; transmitting frame data to an image server; andpresenting frame data by said image server to one or more clients forviewing by one or more users.
 17. A method for capturing, analyzing, andpresenting image data from one or more digital image capture devicescomprising: capturing a plurality of digital image frames; producing aplurality of sequences, said sequences comprising a full frame followedby one or more differential frames wherein pixels in said differentialframes are set to transparent when they have a value within a thresholdof a value of corresponding pixels in a preceding frame; determiningwhether an incident is associated with one or more frames; storing saidplurality of sequences; and presenting one or more sequences to a clientviewer in response to a viewer's request or when an incident isassociated with a sequence.
 18. The method according to claim 17 whereinsaid determining comprises computing a percentage of pixels that havechanged in one frame from one or more preceding frames.
 19. The methodaccording to claim 17 wherein said sequence stored at said image serveris stored in a format designed for still image display on a clientbrowser.
 20. The method according to claim 17 wherein said storingcomprises storage of sequences for which incidents were detected forlater transmission as requested by an image server.